In the field of medical technology, pieces of apparatus are known by which liquids can be withdrawn from a patient and liquids can be provided to the patient. The access to the patient may be gained with a needle or cannula for puncturing vessels in this case. During the examination or treatment, it has to be ensured that the access to the patient remains in proper order. It is therefore necessary for the access to the patient to be monitored.
An application where the safety and reliability of the vascular access has to meet particularly stringent requirements is extracorporeal blood treatment in which blood is withdrawn from the patient via an arterial blood line which has an arterial puncturing needle or cannula, the blood is passed through a dialyser, and is provided back to the patient via a venous blood line which has a venous puncturing needle or cannula. Even though the access to the patient may be regularly monitored by the hospital staff, there is, still a risk in this case that the venous needle or cannula may slip out of the patient's blood vessel unnoticed. Although slipping-out of the arterial cannula causes air to be drawn into the flexible arterial line, which causes an alarm to be given and the treatment to be interrupted; slipping-out of the venous cannula allows for the free flow of blood into the surrounding environment and cannot readily be detected. However, if the slipping-out of the venous cannula is not detected, the patient may bleed to death.
There are different arrangements known in the prior art for solving this problem. Some of these arrangements have recourse to safety devices which are fitted as standard to blood treating machines and trigger an immediate shut-off of the extracorporeal blood circuit if the vascular access is not properly in order. The safety devices which are fitted as standard to treating machines are generally based on monitoring of the pressure in the extracorporeal blood circuit. However, it has been found in practice that slipping-out, particularly of the venous needle or cannula, cannot be detected with sufficient certainty simply by monitoring the pressure in the extracorporeal blood circuit. It is true that some known safety devices are of adequate sensitivity, but they are also very sensitive in the way they react to changes in the patient's position, which often results in false alarms. Another disadvantage is that existing blood treating machines cannot readily be retrofitted with the known monitoring facilities and instead retrofitting calls for laborious and cost-intensive operations to be carried out on the machines.
Known from US 2004/0254513 A1 is an extracorporeal blood treatment apparatus having an extracorporeal blood circuit, which blood treatment apparatus has a monitoring apparatus for the arterial and venous vascular accesses. This known monitoring apparatus has two electrodes, one of which is arranged on the flexible arterial line and the other of which is arranged on the flexible venous line, to make an electrical connection between the liquid in the given flexible line and a monitoring unit. The monitoring unit measures the impedance between the two electrodes, it being concluded that the vascular access is not in proper order if the impedance is not within preset limits. A disadvantage is the fact that the monitoring of the vascular access makes it necessary for there to be additional electrodes and measuring lines. WO 97/10013 describes a monitoring device based on the monitoring of the pressure in the extracorporeal blood circuit, in which the surges of pressure which are generated by the heartbeat and which are propagated along the flexible arterial and venous lines are detected. Absence of the pressure signals is considered to be an indication of faulty vascular access.
WO 2004/110528 A1 describes a device for checking an infusion pump which is based on the monitoring of the sound which the pump emits in operation, which can be sensed in the form of solid-borne sound or airborne sound. It is assumed in this case that, when operating properly, the pump emits sound which has certain characteristics. It is concluded that the pump's operation is faulty when the sound generated by it fails to show these characteristics. Faults with the drive, attributable for example to damaged bearings, can be detected in this way, but so too can blockages of the infusion catheter.
Known from U.S. Pat. No. 5,662,619 is a venous needle for patient access in an extracorporeal blood treatment. The venous needle is ground to a bevel at the distal end. To reduce turbulence as the blood emerges from the needle, lateral openings are provided in the needle and projections projecting into the lumen which point in the opposite direction to the direction of flow are provided downstream of the lateral openings.